1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to an electrophotographic image forming apparatus having a detachable developer cartridge.
2. Description of the Related Art
An electrophotographic image forming apparatus produces an image by forming an electrostatic latent image corresponding to a desired image by scanning light onto a photosensitive medium charged to a uniform electrostatic potential. The latent image is developed by providing toner thereto. The image developed on the photosensitive medium is transferred directly to a sheet of print paper or indirectly through an intermediate transfer. The transferred image is fused by applying heat and pressure thereto.
The electrophotographic image forming apparatus includes a developer cartridge containing a photosensitive medium and toner. The developer cartridge is replaced when the service life of the cartridge ends, and thus installed to be detachable from the main body of the image forming apparatus. Once the developer cartridge is installed, the cartridge has to be fixed tightly at a predetermined position.
An HP printer (such as, for example, HP 3500) employs a coupler to be driven by a drive motor to fix a developer cartridge to a main body. When the developer cartridge has been separated, the coupler is moved back to avoid interfering with the installed developer cartridge. After the developer cartridge is installed and a door is closed, the drive motor is rotated. The coupler is advanced and coupled with one end of a photoreceptor drum, and accordingly the replaced developer cartridge is fixed at a predetermined position. When the door is opened to detach the developer cartridge, the drive motor is rotated in an opposite direction and the coupler is moved back and separated from one end of the photoreceptor drum.
In the above described method of fixing a developer cartridge using a drive motor, when the supply of electricity is interrupted, for example, when a power supply unit of a main body of the image forming apparatus malfunctions, the coupler cannot be moved back, thereby disabling detaching the developer cartridge from the apparatus.
Further, in such a HP printer, the coupler and one end of the photoreceptor drum have complementary shapes. Thus, if the developer cartridge is not installed at a proper position, the coupler and one end of the photoreceptor drum cannot be coupled together, thereby causing developer cartridge installation failure.